This invention relates to improvements in rotary tobacco treatment cylinders and is particularly concerned with the geometry of internal paddles or flights in such cylinders, which are provided to optimize the treatment of tobacco in the cylinder.
In the pre-treatment of tobacco before manufacture within cigarettes, it is necessary to subject it to drying, mixing processes, or conditioning with the addition of fluid; and these are often carried out in a rotary treatment cylinder which is arranged to rotate about a generally horizontal or slightly inclined axis. Such treatment cylinders are provided with internal paddles to provide transport of the tobacco product through the cylinder. In the cases of drying and conditioning it is necessary to maintain the transport time through the cylinder; not only should the average time of the mass of tobacco be maintained but also the time for each individual particle.
Furthermore, the tumbling of tobacco within such a cylinder tends to cause degradation. This degradation is very dependent upon moisture content and increases rapidly with reduction of moisture content below normal cigarette moisture contents of some 13-14%. Thus variation in moisture content in the output from a drying cylinder can be a major contribution to tobacco degradation.
There are several factors which can affect the transport time such as paddle loading, cylinder inclination, drop height, that is to say the height within the cylinder from which the material drops from a paddle to fall back to the wall of the cylinder during the tumbling operation, and the number of drops. However a factor which has been generally overlooked is the consistency which is determined by the release point and which is particularly important in the case of drying.